The present application claims priority under 35 USC 119 to Japanese Patent Application Nos. 2000-280509 filed on Sep. 14, 2000 and 2001-185017 filed on Jun. 19, 2001, the entire contents thereof are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel injection control apparatus, and more specifically, to a fuel injection control apparatus that can determine the amount of fuel injection considering the ambient pressure without using an ambient pressure sensor.
2. Description of the Background Art
When fuel is supplied to the engine by the use of a fuel injection system, an appropriate amount of fuel injection is determined by accurately detecting the operating condition of the engine from the number of engine revolutions, the throttle opening, the negative pressure in the inlet pipe, and the engine cooling water temperature. In order to detect the condition of the engine more accurately, it is often required to detect the ambient pressure separately from the negative pressure in the inlet pipe. However, there are a number of sensors that are integrated in the engine in many cases in order to grasp the operating condition of the engine, and thus it is not preferable to increase the number of the sensor. When a large number of sensors are provided, the construction around the engine becomes complicated. Therefore, free space decreases, and accordingly, the possibility of design is lowered and the cost of production increases. Therefore, it is desirable to develop a method of determining the amount of injection to be supplied without using an ambient pressure sensor.
A fuel control apparatus for complying with this requirement is proposed in Japanese Unexamined Patent Application Publication No. 1-280646. Generally, in the area where the throttle opening is large, the ambient pressure and the negative pressure in the inlet pipe are almost the same. Therefore, in a fuel control apparatus stated in this Patent Application Publication, the area where the difference between the ambient pressure and the negative pressure in the inlet pipe is not more than a prescribed value is determined in advance as an alternative ambient pressure calculating area. When the condition of the engine based on the throttle opening and the number of engine revolutions is maintained in a state to represent the alternative ambient pressure calculating area for a prescribed time period, it is recognized that the negative pressure in the inlet pipe is stabilized, and a predetermined offset value is added to the current value of the negative pressure in the inlet pipe to calculate the alternative ambient pressure value.
In the fuel control apparatus of the related art described above, the area in which xe2x80x9cthe ambient pressure and the negative pressure in the inlet pipe are almost the samexe2x80x9d in the high revolution area of the engine is only the area where the throttle opening is large. In other words, in a state in which the engine is rotated at high speed and the throttle valve is opened to a large extent continues for some period of time, it becomes an alternative ambient pressure calculating area in which xe2x80x9cthe ambient pressure and the negative pressure in the inlet pipe are almost the same.xe2x80x9d
With this related art applied to a motorbike that is driven with the engine rotated at a high speed, if a state in which the throttle opening is large continues, the alternative ambient pressure is calculated, for example, only when it is accelerated for a relatively long time. Therefore, since the possibility of an occurrence of such a state is low, it is anticipated that the possibility of calculating the alternative ambient pressure is also lowered, and thus it is not expected that the accuracy of the alternative ambient pressure is maintained. In addition, since the offset value is added to the negative value in the inlet pipe is a fixed value, improvement of the accuracy cannot be expected.
In addition, since the alternative ambient pressure is calculated when the throttle opening is large, the accuracy for calculating the alternative ambient pressure is low while driving on the downslope, as a consequent, the accuracy of calculating the amount of fuel injection tends to be lowered.
Accordingly, it is an object of the present invention to solve the above-described problem, and to provide a fuel injection control apparatus in which an accurate amount of fuel injection can be calculated by the alternative ambient pressure value with its accuracy improved.
In order to achieve the object described above, the first feature of the present invention is a fuel injection control apparatus for correcting the basic injection time period calculated from the number of engine revolution and the throttle opening by the correction expression including the value of the ambient pressure to calculate the corrected injection time period, comprising area determination means for determining the division of the area defined as a function of the number of engine revolution and the throttle opening in which the engine condition resides out of a plurality of divisions divided based on the offset value that is the difference between the ambient pressure determined under the reference ambient pressure in advance and the negative pressure in the inlet pipe according to the number of engine revolution and the throttle opening. A calculating means is provided for calculating the base value for calculating the alternative ambient pressure by adding the offset value described above provided for each area determined by the area determination means to the negative pressure in the inlet pipe. Ambient pressure value determination means is provided for determining the base value for calculating the alternative ambient pressure as a value of the ambient pressure when the difference between the last determined value of the ambient pressure and the base value for calculating the alternative ambient pressure is not more than the predetermined value.
According to a first feature, a plurality of offset values each of which is the differences between the ambient pressure and the negative pressure in the inlet pipe are provided so that the offset value corresponding to each area determined by the number of engine revolutions and the throttle opening can be selected and the fuel can be corrected accurately according to the condition of the engine.
A second feature of the present invention is that the ambient pressure value determination means determines the base value for calculating the alternative ambient pressure as an ambient pressure value when the base value for calculating the alternative ambient pressure exceeds the last determined value of the ambient pressure.
According to the second feature, since the base value calculating the alternative ambient pressure is reliably renewed by the ambient pressure value at the time when the base value for calculating the alternative ambient pressure exceeds the last determined value of the ambient pressure, for example, the accurate value of the ambient temperature can be set during traveling on the downslope where the air pressure tends to increase.
The present invention has a third feature in that the ambient pressure value determination means is constructed wherein the maximum value of the base value is determined for calculating the alternative ambient pressure within a predetermined time period from the moment when the last value of the ambient pressure is determined as the ambient pressure value. Since the ambient pressure value is renewed by the maximum value of the base value for calculating the alternative ambient pressure detected within the predetermined time period, for example, the ambient pressure value is prevented from being determined to the value lower than the actual value of the ambient pressure under the influence of the base value for calculating the alternative ambient pressure that tends to be lowered on the upslope.
The fourth feature of the present invention is opening variations detecting means for detecting variation of the throttle opening wherein the ambient pressure value determination means is energized when the variation is within the predetermined value. According to the fourth feature, the accurate ambient pressure value can be obtained since the ambient pressure value is not renewed when the throttle opening is suddenly changed, which may cause instability of the negative pressure in the inlet pipe.
The fifth feature of the present invention is that calculating means that is constructed in such a manner that when the vehicle speed exceeds the predetermined value, the traveling pressure value corresponding to the vehicle speed is calculated to add the ambient pressure value. The sixth feature of the present invention is that storage means for setting the traveling pressure value under the air pressure of 760 mmHg corresponding to the vehicle speed is provided and that the calculating means uses the traveling pressure value read from the storage means according to the vehicle speed. According to the fifth and sixth features, the ambient pressure value can be determined considering the influence of the traveling pressure that emerges when the vehicle speed is high. In addition, the present invention has a seventh feature in that the reference ambient pressure value is an air pressure corresponding to 760 mmHg.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.